By studying fossils, scientists have learned that

By studying fossils, scientists have learned that both animals and plants have changed over time.

Explanation:

By studying the fossils, the scientists learn about their life in the past and how plants and animals are related to each other. By using the information how and where they lived, we can find out ancient environments.

Scientists study about fossils from variety of environments to give information about animals and plants that are living at a particular time at past. The study of fossils and the rocks that contain them occurs at both doors and laboratory.

the only other powers were germany russia and uk and they were too busy fighting each other wearing each other down   that the us was becoming strong and they were becoming weaker